The invention relates generally to strip chart recorders and similar apparatus. More particularly, the invention relates to apparatus and methods for detecting or monitoring one or more attributes of a strip chart recorder paper supply, such as, for example, the quantity of paper available.
Strip chart recorders commonly use a paper supply that consists of a continuous web of paper that may be stored on a roll or stacked as connected sheets or pages. Individual pages may be conveniently separated by the use of perforations or tear lines. It is important, however, that the paper supply not be exhausted during operation of the recorder. Several techniques are known for detecting the end of a paper web supply, including mechanical arms, mechanical arms in combination with a variable resistance, visual monitoring, or edge line markings that indicate the last six feet or so of paper remaining.
These known techniques have many drawbacks, one of the most important being that usually some type of visual verification must be made at the time that the paper supply is about to be exhausted. Furthermore, an operator relying on the edge line marking visual technique must not only be present, but also will not know necessarily how close the paper supply is to the end of the roll. Thus, if a particular recording operation requires more paper than the edge marked pages, an operator cannot know if sufficient paper is available. Even if the edge markings are detected electronically, the operator cannot know with certainty how much paper remains until the edge markings are detected. The other techniques generally do not have a high degree of precision. Furthermore, none of these previous techniques of quantity detection can be used for other attributes of the paper such as the type of paper, sensitivity of the paper, or paper serial number.